Chief Election Commissioner Nasim Zaidi on Saturday ruled out going back to the paper ballot system, saying paper trail machines will usher in more transparency in future elections.

"Once the EVMs are used with VVPATs (or paper trail machines) where a voter can see (cross check) the vote he has cast, it will usher in more transparency. Then there is no scope of going back to ballot (paper) system," he told reporters here, on a day when no opposition party took part in the EVM challenge held by the Election Commission to allow parties to try and hack the electronic voting machines.

The voters see voter-verifiable paper audit trail (VVPAT) slip for seven seconds. The slip then drops in a box but the voter cannot carry it away. Parties want the slip to be visible for 15 seconds.

Zaidi said the EC has already announced that in all future elections to Lok Sabha and state assemblies, VVPAT machines would be attached to all EVMs.

The process would begin with Himachal Pradesh and Gujarat polls later this year.

With the Centre releasing Rs 3,173 crore for acquiring 16.15 lakh VVPAT machines, these will be used in all polling stations in the 2019 Lok Sabha polls. The production will start in August and delivery would be made in September, 2018.

Over a dozen opposition parties, including the Congress, the BSP, SP, the Left, DMK, and JD-U, had urged the EC in April to revert to the paper ballot system in future elections, saying tampering allegations have created "trust deficit" on the reliability of the EVMs.